“Council of Nikaea (~005.M31): Emperor bans Legion Librarius after Magnus’ warnings and debates. Pre-Nikaea: Astartes psykers common and celebrated. Post-Nikaea: psychic powers forbidden for Space Marines—violators face censure, mind-wiping, or execution. During Heresy, traitors ignore it openly; loyalists risk it only in extremis with heavy consequences and Perils of the Warp.”